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Fatigue Crack Propagation in Crystalline Polymers and Composites.
LEHIGH UNIV BETHLEHEM PA MATERIALS RESEARCH CENTER
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As polymers are used to an increasing extent in load-bearing applications, often under cyclic or repetitive loads, an understanding of fatigue behavior is important. Since all polymers contain flaws that may, under appropriate conditions, develop into catastrophic cracks, the fatigue crack propagation FCP response is of particular interest to the engineer. The role of polymer structure and composition in the kinetics and energetics of FCP is, in turn, of fundamental chemical and physical concern. The principal goal was to elucidate the role of polymer structure, composition, and morphology on the kinetics, energetics, and mechanisms of FCP in typical crystalline polymers, as well as the effects of external variables such as frequency and stress range. Emphasis was placed on the effects of molecular weight, percent crystallinity, morphology, and where appropriate, environment. With respect to reinforced polymers, the emphasis was on the role of fiber content, fiber orientation, interfacial adhesion, and matrix properties. In all cases, the characteristics of the process or damage zone at the crack tip was determined wherever possible.
APPROVED FOR PUBLIC RELEASE